Generally, a transmission system for a digital signal comprises a transmitter and a receiver connected by a transfer bus. With reference to FIG. 1 a transmission system of the above type comprising at least one transmitter 1 for a digital signal is schematically represented by reference 20.
In particular, in the example shown in FIG. 1, the transmitter 1 comprises three drivers 1a, 1b, 1c. The transmission system 20 also comprises a receiver 2 for receiving this digital signal, and at least one transfer bus 3 for connection of the transmitter 1 to the receiver 2 and the transmission of the digital signal.
In particular, the transfer bus 3 schematically shown in FIG. 1 is aligned with one or more additional transfer buses 5 and 6, similarly structured and integrated in an integrated circuit 21.
To speed up the transfer of the digital signal from the transmitter 1 to the receiver 2 transmission systems 20 are known to adopt techniques for regulating the ratio RC (Resistance-Capacity) of the transfer bus 3. These techniques suitably vary the resistance of the transfer bus 3, and allow the adjustment of the transfer speed of the digital signal.
Although advantageous, the transmission systems based on RC regulation of the transfer bus are affected by the physiological RC limit of the integration process. For example, considering the use of a transfer bus 3 with length equal to 6 mm, for a process wherein the resistivity of the material making up this transfer bus is 80 mΩ/squared and has an area capacity of 110 fF/u2, there will be an RC limit or asymptotic of about 60 ps.
This estimate is not significant since it implies power being input into a transfer bus 3, and a practically unlimited width of the above transfer bus. In a realistic case the transfer bus 3 has a width of 2 u dedicated to the digital signal to be transmitted, and it produces a measured delay with a voltage equal to half a supply voltage (VCC/2) of 400 ps.
The speed of the digital signal on the transfer bus 3 is also influenced by the transmission of digital signals onto the additional transfer buses 5 and 6, since these additional buses 5 and 6 interfere with the transfer bus 3, causing a slowdown thereof in the propagation of the digital signal.
The International Application No. WO98/40980 discloses an apparatus for an electrical line communication between a transmitter and a receiver. Such an application is intended to transfer high speed data over long distances, using couplers at each of two or more locations along the electrical line.